1. Technical Field
The present invention relates to a resonator element, a resonator, an electronic device and an electronic apparatus.
2. Related Art
In recent years, as a piezoelectric vibration device tends to be small, it is desirable that a CI (crystal impedance) value be decreased. It is known to adopt a mesa structure in order to decrease the CI value and confine vibration energy.
JP-A-2007-124441 discloses a piezoelectric resonator element that defines an optimum value of an etching amount from a substrate for obtaining a mesa structure. More specifically, in JP-A-2007-124441, when the etching amount is Md, a length of a long side of a quartz crystal substrate is x, and a thickness of a vibration section is t, if a percentage y of a ratio to the thickness t of an etching amount Md of a step portion with reference to the thickness t is set, a relationship of y=−1.32×(x/t)+42.87 is satisfied. Therefore, it is disclosed that a minimum etching amount Md can be selected to allow a characteristic change in the CI value to be flat.
Further, JP-A-2008-263387 discloses that not only an optimum value of the etching amount from value of the substrate, but also a range of the length of the long side in an application range of conductive adhesive applied when the piezoelectric resonator element is mounted on amount substrate are defined to suppress a binding of an unnecessary mode, and to promote a decrease in the IC value.
Further, JP-A-2010-28610 discloses that by defining the length from the end of the vibration section to the end of the excitation electrode, the characteristic deterioration such as the increase in the CI value can be suppressed.
Therefore, the decrease in the CI value has been contemplated from various viewpoints.